The present invention provides the novel crystalline bis hydrochloride monohydrate salt of the imidazopyridine RSV (i.e., respiratory syncytial virus) Fusion Inhibitor of the formula 
which exhibits superior physical stability to other salts, and significantly improved aqueous solubility/dissolution behavior and bulk characteristics compared to the free base. The bis hydrochloride monohydrate salt is thus useful for pharmaceutical dosage forms of the above indicated RSV Fusion Inhibitor, particularly for oral dosage forms.
Commonly-owned U.S. patent application Ser. No. 09/840,279 filed Apr. 3, 2001 discloses a series of imidazopyridine and imidazopyrimidine antiviral agents reported to have a high degree of inhibitory activity against the RSV virus. One of the agents included within the scope is the compound having the structural formula 
This application discloses the free base form of imidazopyridine derivatives such as compound I and also various pharmaceutically acceptable acid addition salts. While several organic and inorganic salts are mentioned as possible salt-forming agents, including hydrochloric acid, there is no mention of the particular bis hydrochloride monohydrate salt which is the subject of the present application.
The present invention provides the bis hydrochloride monohydrate salt of compound I above having the structural formula 